Here are a couple basics: Round Up only kills existing plants, not seeds. Preemergent herbicides do not kill seeds, either. What they do is prevent a germinated seed from taking root.

Now is a terrible time to seed new grass. Can you wait until fall? If you do it now the summer heat will take out the tender new grass. Or, since it is a small area you could put sod in for not too much cost. Sod is already established and should survive.

Do not till in preparation for grass. Scrape it flat, but don't till. To get rid of weeds, mow everything down and water it 2x to 3x per day for only 5 minutes. This will germinate all the crabgrass and dandelion seeds. After a week spray with Round Up to kill all those weeds. Continue watering daily to sprout any late bloomer seeds and spray with Round Up again. After the second Round Up app you can put down either sod or seed. You do not need to cover it with straw.

Don't add topsoil unless the area is lower than the rest of the lawn. Otherwise this area will be higher than the rest of the grass and will dry out faster.

Hopefully your lawn service is not spraying herbicide 6x per year. At most they should spray twice. Those other apps are likely to be fertilizer. If you are already mowing and watering the lawn, you can do the fertilizer and herbicide yourself and save a few hundred (or whatever they're charging). Fertilizer goes down 3x per year (Memorial Day, Labor Day, and Thanksgiving). Herbicide goes on in late April and maybe again in May if you missed some. There's not too much too it.

Thanks for your wonderfully detailed response, dchall.

1. "Round Up only kills existing plants, not seeds. Preemergent herbicides do not kill seeds, either. What they do is prevent a germinated seed from taking root." My lawn guys ended up spraying weed-b-gon on the flower bed after they had wiped it clean. From the weed forum here, and from other forums, I gather this was a useless thing to do since weed-b-gon is a post-emergent contact poison. Also I am told I should now wait for 3-4 weeks before planting/seeding in this area. (I was going to keep a small portion of the flower bed for planting rose bushes). I assume based on this advise weed-b-gon does impact the ability of seeds/plants to germinate/take root?

2. Is putting tarp (or heavy duty black plastic sheeting) over the area (about 325 sq ft) a good alternative (to roundup) for suppressing weed growth?

3. "Hopefully your lawn service is not spraying herbicide 6x per year. At most they should spray twice. Those other apps are likely to be fertilizer." You are correct. I will certainly look into taking this on myself.

Thanks!!